Magnetic tunneling junctions (MTJs) are fabricated using CoFe-Ru-CoFe artificial antiferromagnet (AAF) sandwiches as a hard-magnetic reference layer and plasma-oxidized aluminum as a tunnel barrier. Tailoring the magnetic properties of the artificial antiferromagnet reference layer allows an on-chip magnetization (initialization) of individual junctions, which makes it possible to build monolithic bridges in a Wheatstone arrangement without multiple mask process steps or on-chip heating elements. The functionality of an angular field sensor based on this concept is demonstrated in detail. The thermal stability of such a sensor is investigated and the limitations of the concept are discussed.